In recent years, there has been proposed an ultra-small radio base station (femto radio base station) BTS which provides a cell (femtocell) having a radius of approximately several tens of meters.
Since the femtocell under control of the femto radio base station BTS is utilized by a small number of mobile stations UEs, a high-speed service using a wide frequency band can be provided.
In addition, since the femto radio base station BTS is installed in a subscriber premise or the like, the femto radio base station BTS is believed to provide new services merged with a fixed communication service subscribed to by a subscriber.
In a general household, a small office or the like, a single or multiple femtocells can form a private area specific to a particular user by minimizing the coverage area of each femtocell, or by applying an inexpensive local IP line to connection between each femto radio base station BTS and a radio network controller RNC.
Meanwhile, a discussion is being made to provide “user exclusive services,” that is, to provide particular users with a charging system special to a femtocell, an added function only in a femtocell, and the like.
In the femtocell providing such user-exclusive services, a mobile station UE of a particular user allowed to access the femtocell is desired to be preferentially guided to the femtocell.
By referring to FIG. 1 and FIG. 8, a description is given of an operation of performing a location registration of a mobile station based on a conventional W-CDMA scheme.
In examples in FIG. 1 and FIG. 8, a description is given of an operation performed when a mobile station UE in a camp-on state in a macrocell 1 operated. at a frequency f1 moves to a macrocell 2 operated at a frequency f2. Note that the macrocell 1 and the macrocell 2 belong to different location registration areas.
As shown in FIG. 8, in Step S3001, when detecting a change of a location registration area on which the mobile station UE visits after moving to the macrocell 2, the mobile station UE transmits “RRC CONNECTION REQUEST” requesting an establishment of an RRC connection, to a radio network controller RNC through the macrocell 2.
In Step S3002, the radio network controller RNC transmits “RRC CONNECTION SETUP” to the mobile station UE. In Step S3003, the mobile station UE transmits “RRC CONNECTION SETUP COMPLETE” to the radio network controller RNC, and thereby the establishment of the RRC connection between the radio base station RNC and the mobile station UE is completed.
In Step S3004, the mobile station UE transmits a location registration request signal (ROUTING AREA UPDATE REQUEST) to the radio network controller RNC by using “INITIAL DIRECT TRANSFER” which is an RRC message.
In Step S3005, the radio network controller RNC having received “INITIAL DIRECT TRANSFER” forwards the received location registration request signal by using “INITIAL UE MESSAGE” which is an RANAP message.
After authentication and ciphering processing for the mobile station TIE succeeds in Step S3006, an exchange transmits a location registration response signal to the radio network controller RNC by using “DIRECT TRANSFER” which is an RANAP message in Step S3007. The location registration response signal is for permitting location registration to register the mobile station UE for a location registration area to which the macrocell 2 belongs. In Step S3008, the radio network controller RNC forwards the received location registration response signal to the mobile station UE by using “DL DIRECT TRANSFER” which is an RRC message, and thereby the location registration of the mobile station UE for the location registration area to which the macrocell 2 belongs is completed (Step S3009).
In Step S3010, the exchange sends the radio network controller RNC “IU RELEASE COMMAND” which is an RANAP message instructing release of the aforementioned RRC connection.
In Step S3011, the radio network controller RNC having received “IU RELEASE COMMAND” transmits “RRC CONNECTION RELEASE” to the mobile station UE and thereby releases the aforementioned RRC connection.
In 3GPP specifications, the radio network controller RNC is configured to designate a camp-on frequency of the mobile station UE by using such “RRC CONNECTION RELEASE.”